Bead and process for removing dissolved metal contaminants

ABSTRACT

A bead is provided which comprises or consists essentially of activated carbon immobilized by crosslinked poly(carboxylic acid) binder, sodium silicate binder, or polyamine binder. The bead is effective to remove metal and other ionic contaminants from dilute aqueous solutions. A method of making metal-ion sorbing beads is provided, comprising combining activated carbon, and binder solution (preferably in a pin mixer where it is whipped), forming wet beads, and heating and drying the beads. The binder solution is preferably poly(acrylic acid) and glycerol dissolved in water and the wet beads formed from such binder solution are preferably heated and crosslinked in a convection oven.

BACKGROUND OF THE INVENTION

The present invention relates generally to beads, methods of makingbeads, and methods of using beads to remove metal and other ioniccontaminants dissolved in aqueous solutions. The beads preferablyinclude activated carbon and a binder and the activated carbon, andpreferably the binder, are capable of sorbing dissolved metal ions.

DESCRIPTION OF RELATED ART

The removal of metal contaminants from aqueous wastes such as acid minedrainage/water and industrial waste water such as metal finishing wastewater and municipal waste water, is an important environmental andeconomic issue. Some of the metal ions are toxic and some are valuable.In the chemical area of toxic metal recovery from dilute aqueous steams,the techniques of recovery have most commonly been by chemicalprecipitation, ion exchange, reverse osmosis, electrodialysis, solventextraction (liquid ion exchange), and chemical reduction. (See U.S. Pat.No. 5,279,245). However, these procedures are characterized by thedisadvantages of incomplete metal removal, high reagent and energyrequirements, and generation of toxic sludge or other waste productsthat must be disposed of, and these disadvantages are particularlyconspicuous at the low metal concentrations often encountered in wastewaters, where federally-mandated cleanup standards dictate thateffluents discharged to public waters generally contain less than 1 mg/Lof metals such as copper, zinc, cadmium, lead, mercury and manganese.

Thus there exists a need for a more effective metal ion sorbentimmobilized in a matrix in a mechanical shape such as a bead and for aneffective, less-hazardous method of making such beads using binders ormatrix materials which do not involve hazardous materials. Preferablythe binder or matrix material itself is capable of sorbing The sorbentshould be able to remove contaminants from both wastewater and potablewater. There is a further need for a process which makes beads which areuniformly spheroidal. Non-spheroidal beads tend to pack asymmetrically,tending to cause water flowing there-through to flow in certainchannels, rather than uniformly over all the beads. Among the objects ofthe present invention are to answer these needs.

SUMMARY OF THE INVENTION

A bead is provided which comprises activated carbon and a binder, thebinder preferably being poly(carboxylic acid) effectively crosslinkedwith a crosslinking agent. The activated carbon is effectivelyimmobilized in the bead. The bead is capable of sorbing a metal or otherions dissolved in a dilute aqueous solution at a concentration of lessthan 10 ppm, said metal or ion being selected from the group consistingof lead, copper, silver, chromium, cobalt, uranium, mercury, nickel,arsenic, aluminum, cadmium, iron, manganese, and zinc. A method ofmaking a metal-ion-sorbing bead is also provided. The method comprises:

(a) combining, activated carbon, such as bituminous coal-based powderedcarbon, and binder solution into a mixture, the binder solutioncomprising poly(carboxylic acid) and a crosslinking agent;

(b) forming the mixture into a first bead;

(c) heating said first bead to effectively crosslink the poly(carboxylicacid) with the crosslinking agent to form an effectively crosslinkedbinder.

A method of using the bead for removing a metal or metalloid from adilute aqueous solution is also provided.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an elevational view with the exterior in section of a pinmixer for use in the present invention.

FIG. 2 is a perspective view with part of the casing cut away of a dryerfor use in the present invention.

FIG. 3 is a perspective view showing in more detail one of the trays ofthe dryer of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The terms sorb, sorbing, and sorption are used in the broad sense and asused herein are defined to include all forms of metal and othercontaminant uptake and attachment, whether by adsorption, absorption,ionic bonding (including ion exchange), among other forms of metaluptake and attachment. Parts per million (ppm) and parts per billion(ppb) are parts by weight.

As used herein, the following terms have the following meanings.“Poly(carboxylic acid)” means a polymer including monomeric units whichhave a carboxylic acid functional group. The preferred poly(carboxylicacid) of the present invention is poly(acrylic acid). “Polyalcohol”means an organic compound that contains more than one hydroxy group.Glycerol and ethylene glycol are polyalcohols. The beads of the presentinvention includes poly(carboxylic acid) beads, sodium silicate beads,and polyamine beads, as further described herein.

The preferred binder solution is poly(carboxylic acid) and acrosslinking agent in water. The crosslinking agent crosslinks thepoly(carboxylic acid) as described hereinafter. The poly(carboxylicacid) is preferably poly(acrylic acid), less preferably poly(methacrylicadd), less preferably those poly(carboxylic adds) which are likepoly(acrylic acid) but which have fewer carboxylic acid functionalgroups per carbon chain length. More carboxylic acid functional groupsper unit weight is advantageous, since there is more metal ion uptakecapacity per unit weight. The poly(carboxylic acid) utilized preferablyhas a molecular weight of at least 10,000 and preferably not more than500,000. More preferably the molecular weight is at least 80,000 and notmore than 400,000, more preferably between 200,000 and 300,000. Thepreferred poly(carboxylic acid) is poly(acrylic acid), which isavailable from BF Goodrich Specialty Chemicals Cleveland, Ohio, asCarbopol ISX-1794 (unneutralized version)(this product is, by weight,75% water and 25% poly(acrylic acid) with the poly(acrylic acid) havinga molecular weight of about 250,000, which is preferable). Thecrosslinking agent is preferably polyalcohol. The polyalcohol ispreferably glycerol, less preferably ethylene glycol, 1,2-propanediol,or 1,3-propanediol, less preferably poly(vinyl alcohol). Thecrosslinking agent is less preferably a polyamine, such as poly(ethyleneimine), a tri-amine, or a diamine such as diamino butane.

The activated carbon to be used in the present invention is preferably apowdered bituminous coal-based activated carbon (PAC). If the endproduct is intended for use with potable water, the carbon should bespecifically designated for the use in the treatment of potable waterand have ANSI/NSF certification. Such carbon is available from CalgonCarbon Corporation, called WPH powdered activated carbon. Other lesspreferable types of carbons include coconut shell based and wood basedcarbon. The carbon should have a minimum Iodine Number of 600 mg/g, morepreferably 700 mg/g, most preferably 800 mg/g or higher. The pHassociated with the carbon is preferably neutral or slightly acidic,less preferably basic.

The preferred binder solution is, by weight, about 60-98%, morepreferably about 75-85%, water, about 2-40%, more preferably about5-20%, more preferably about 10-15%, poly(carboxylic acid), and about0.1-15%, more preferably about 0.5-3%, more preferably about 1-2%polyalcohol or other crosslinking agent. A preferred binder solution is,by weight, about 0.1-15%, more preferably about 0.5-3%, more preferablyabout 1-2%, glycerol, about 2-40%, more preferably about 5-20%, morepreferably about 10-15% poly(acrylic acid), and about 60-98%, morepreferably about 75-95%, more preferably about 80-85% water. A preferredbinder solution, by weight, is 1.0% glycerol, 57.3% Carbopol ISX-1794(unneutralized, which is 75% water), and 41.7% water, mixed at roomtemperature (72° F.).

A less preferred binder solution is a solution of sodium silicate inwater. A starting material for this is product STIXSO RR from The PQcorporation Valley Forge, Pa. 19482, which is by weight 9.2% Na2O, 30%SiO₂, and 6.8% water. Product STIXSO RR is diluted at 70°-85° F. withwater (preferably about 264 g STIXSO RR to 1000 g water, although it maybe made more or less diluted) to provide the binder solution. Anothersodium silicate starting material is Sodium Silicate N from The PQcorporation, which is 8.9% Na2O, 28.7% SiO₂, and 62.4% water.

An alternative binder solution is polyamine and a crosslinking agent inwater. The polyamine is preferably polyethylenimine (preferably60,000-100,000 MW) and the crosslinking agent is preferably adicarboxylic acid where the two groups are joined by a straight-chainalkane radical and each acid group is located at a terminal carbon,preferably glutaric acid, less preferably succinic acid, less preferablymalonic acid. The polyethylenimine can be utilized in some applicationswith out the crosslinking agent. A preferred binder solution is, byweight, 5-40% preferably 12-27%, more preferably 18%, polyethylenimine,0-3%, more preferably 0.3-2%, more preferably 0.5%, glutaric acid, andthe balance water. The invention is preferably made from a powderedactivated carbon, which is agglomerated with the binder to the desiredsize of the final product. This powdered carbon is preferably 90%smaller than 100 mesh, more preferably 90% smaller than 200 mesh, andmost preferably 90% smaller than 325 mesh. The product can be made froma granular carbon in which case the raw material carbon is near the sizerange of the desired end product. This size is typically in the range of−20+50 mesh, therefore the starting carbon should be in that same rangeor slightly smaller, such as −40+80 mesh.

The screened activated carbon and binder solution are preferably mixedand processed in an apparatus for mechanical spheronization to yield themechanical shapes of granules or beads disclosed herein. An apparatusfor mechanical spheronization produces spheroidal beads or granules. Asused in the specification and claims, an apparatus for mechanicalspheronization includes a pin mixer, and an Eirich mixer in combinationwith a disk pelletizer or spheronizer. The activated carbon ispreferably fed via a regulated screw feeder such as an Accuson screwfeeder to a pin mixer. A preferred pin mixer is available from MMC MarsMineral, P.O. Box 719, Mars, Pa. 16046, such as their Model 12D45L orModel 8D36L. Pin mixers are known devices, the details of which areknown and are incorporated by reference. With reference to FIG. 1, thepin mixer has a cylindrical, stationary shell horizontally oriented witha length-to-diameter ratio of preferably between 2 and 5. Upperhemispherical shell 10 and lower hemispherical shell 12 form thecylindrical shell. Upper hemispherical shell 10 may be hinged so themixer may be opened. The interior surfaces of the shells 10 and 12 arelined with sheet rubber 14 and 16. Inside the shell along its centralaxis is a shaft 26 with radially-extending rows of metal pins or rods28. The pins 28, which are means to impart high shear forces arearranged in a staggered, overlapping double helical pattern and extendinto the chamber when the mixing takes place, the mixer shell enclosingthe chamber. There is a close tolerance between the tips of the pins andthe inside of the mixer shell, for example. {fraction (3/16)} inch.Shaft rotational speed, and therefore tip speed, is high (severalhundred RPM, a typical speed being 900 to 1700 RPM.) Optionally, a vent24 may be provided. The pin mixer imparts high shear forces(particularly by means of its pins) and rotational forces as well asplug flow characteristics to the material being mixed.

The activated carbon is entered at inlet 20, moved forward by vanes 30,and the liquid binder solution is sprayed onto the activated carbon fromnozzle 32. Additional nozzles can optionally be placed at otherpositions along the top of shell 10. The injection pressure of bindersolution is preferably about 15 PSI, but will vary depending onviscosity. Preferably about 150 lbs. of the above-referenced 57.3%Carbopol, 1.0% glycerol solution is added per 100 lbs. of activatedcarbon, depending on moisture content of the activated carbon.

Preferably the material inside the pin mixer is 140°-170° F.; generallyit takes about 20 minutes of operation to get to this temperature(frictional forces leading to temperature rise). Alternatively steam maybe injected to raise the temperature or other means may be used.

The activated carbon/binder solution mixture or media is whipped andmixed and rapidly stirred and high shear forces are imparted with rigidmembers in an air atmosphere (and not underwater) by the pins 28 as itmoves as a plug flow or with plug flow through the shell in thedirection indicated by arrow 35 to the bottom outlet 22, where it exitsin the fore of wet spheroidal beads or granules (typically about 0.3 to1.0 mm in diameter) having a temperature typically of about 160° F., anda moisture content, for poly(carboxylic acid) binder solution, ofpreferably about 45-60% by weight, and a moisture content for sodiumsilicate binder solution, of preferably about 60-70%, more preferably65-68%, more preferably 66% by weight.

It is important to control three variables: dry feed rate (rate at whichactivated carbon is fed in), binder feed rate (rate at which bindersolution is added), and the temperature of the material inside the mixer(this temperature being largely influenced by the RPM rate, due tofrictionally generated heat). These rates will vary depending on anumber of factors, principally the size of the pin mixer. Preferably, apressure gauge and temperature gauge are installed on the cylindricalshell to monitor operating conditions and parameters.

One advantage of a pin mixer is that residence time or retention time ofthe material in the mixer is controlled and limited, since the materialmoves as a plug flow down a path and then exits.

Alternatively, the wet beads may be produced by processing the activatedcarbon and binder solution through an Eirich mixer and then through adisk pelletizer or spheronizer. An Eirich mixer is a high shear mixeravailable from the Eirich Company in Germany. The details and operationof an Eirich mixer are known and readily available and are incorporatedby reference. It has a bowl or chamber in which the activated carbon andbinder solution are placed. The bowl turns in one direction and anS-shaped blade which descends into the bowl rotates at a high speed inthe other direction, mixing and whipping and rapidly stirring with arigid member the contents of the bowl and imparting high shear forces tothe mixture. The Eirich mixer produces wet beads which typically aremisshapen and not sufficiently round. The beads are then preferablytaken from the Eirich mixer and are placed in an apparatus to improvethe spheroidalness of the wet spheroidal beads. Suitable such apparatusinclude a disk pelletizer available from MMC Mars Mineral, and aspheronizer available from Niro, Inc., Columbia, Md. The details andoperation of these devices are known and readily available and areincorporated by reference.

The wet poly(carboxylic acid) beads after exiting the pin mixer orapparatus for improving spheroidalness are heated to crosslink thepoly(carboxylic acid) using the polyalcohol or other crosslinking agentto form a tough, strong, resilient, water insoluble, polymeric, plasticmatrix or binder or structure for the bead. The activated carbon iseffectively immobilized in the bead so that the bead may performeffectively. When the crosslinking agent is polyalcohol, the alcoholfunctional group reacts with the carboxylic acid functional group toform a linkage, which reaction is repeated at many sites, yielding anester crosslinked poly(carboxylic acid). Preferably, only the minimumnumber of carboxylic acid function groups are utilized in forming esterlinks or other links, since those remaining are then available for ionexchange, that is, metal ion uptake or sorption. Thus the amount ofpolyalcohol or other crosslinking agent used should be minimized. Thepoly(carboxylic acid) is effectively crosslinked when sufficient esteror other types of linkages have been formed to provide a polymericmatrix which provides effective structural support for the bead. If thecrosslinking agent is a polyamine, the polyamine reacts with thepoly(carboxylic acid) to form amide crosslinks. Too much crosslinkingleads to brittleness and less ion exchange capacity, too littlecrosslinking leads to insufficient structural support. The extent ofcrosslinking can be controlled by varying the heating method, theheating time, the heating temperature, and the concentrations of thereactants.

The heating/crosslinking step for the wet poly(carboxylic acid) bead ispreferably carried out by heating in a convection oven or other heatingmeans. In a convection oven the crosslinking step is preferably carriedout at a temperature of about 250°-350° F. for about 2 to 3 hours.Heating time depends principally on the temperature selected and initialmoisture content of the beads. In a preferred process, heating is at300° F. for 2 hours in a convection oven, with the beads having amoisture content of about 1% by weight when the reaction is done.Alternatively the crosslinking step can he accomplished using othermeans, such as a hot air dryer, a TURBO-Dryer as discussed herein, or atumble dryer.

After the crosslinking step, the beads are preferably separated by sizeinto large (retained on U.S. Standard Sieve No. 20), small (passesthrough US. Standard Sieve No. 50), and medium (passes through No. 20above but is retained on No. 50 above, i.e. −20+50 mesh). The beads maythereafter be stored dry and are believed to have an indefinite shelflife.

The poly(carboxylic acid) beads preferably have the following physicalcharacteristics: relatively spheroidal, bulk density—about 20-25lbs/ft³, 0 to 10, more preferably 0 to 5, more preferably 1 to 3 weightpercent water, 65 to 94, more preferably 74 to 88, more preferably 78 to84, weight percent activated carbon, and 4 to 25, more preferably 8 to20, more preferably 14 to 19, weight percent crosslinked poly(carboxylicacid) binder. The poly(carboxylic acid) beads will tolerate withoutmaterial damage temperatures up to 250° F., and they operate at a pHrange preferably of 1.75 to 10, more preferably 4 to 9, more preferably6.5 to 8.5. The beads have an internal porous structure so that watermay penetrate and contact the activated carbon and binder throughout thebead, both the activated carbon and poly(carboxylic acid) binder havingmetal ion uptake capacity. This bead is more porous than the sodiumsilicate bead described herein. The disclosed poly(carboxylic acid) beadhas advantages over the herein disclosed sodium silicate bead. It isphysically stronger and more durable than the sodium silicate bead, iswater insoluble, can operate at higher, temperatures, and has inherentlybetter metal uptake capacity because the poly(carboxylic acid) binderitself has metal uptake capacity and is a cation exchange material.

The wet sodium silicate beads after exiting the pin mixer or apparatusfor improving spheroidalness are transported via conveyor or other meansto a dryer, preferably a TURBO-Dryer available from Wyssmont Company,Inc., Fort Lee. N.J. or a dryer available from Carrier Corporation, suchas their Model QAD-1260S-IO. With regard to FIGS. 2 and 3, there isshown a TURBO-Dryer 40 from Wyssmont Company, Inc. Dryer 40 has a casing42 containing trays 44. A tray is shown in more detail in FIG. 3. Thewet beads enter at inlet 46 and are transported along a pathwayindicated by 48 to outlet 50. With regard to FIG. 3, the tray 44, whichrotates in the direction indicated by arrow 56, has a fan 52 with blades54 blowing hot air radially outward across the beads which are in ridgedpanes 58. The beads fall from the tray above to location or position 60,are leveled by stationary leveler 62, and are carried around on the trayin ridged panes 58 until they meet stationary wiper 64. Stationary wiper64 wipes the beads from the ridged panes 58 as the ridged panes passunderneath and drops the beads through the open slots 66 as they passbeneath, the beads then dropping to the tray below, as indicated at 68.

In the TURBO-Dryer the sodium silicate beads are dried with hot air(about 200° F.) and rolled, which maintains and enhances the spheroidalshape, which is the preferred shape. Other dryers known in the art canbe used, preferably those which also roll the material. The sodiumsilicate beads are dried to moisture content of preferably between about5% and about 10% by weight. The beads shrink as they dry. Air drying isnot preferred; it is time-consuming, inefficient and does not roll thesodium silicate beads.

The dried beads, made with any of the mentioned binders, are preferablyspheroidal, less preferably globular or orbular, are then preferablyscreened to sort by size. Typically there are three sizes: large (passesthrough U.S. Standard Sieve No. 8 but is retained on U.S. Standard SieveNo. 20. i.e., −8+20), medium (−20+50), and small (−50+150), althoughlarger and smaller beads may also be used. The openings in U.S. StandardSieve Nos. 8, 20, 50 and 150 are approximately 2360, 850, 300, and 100microns, respectively. These screened beads are dimensionally stable andhave a bulk density of about 20-30, more preferably about 25 lbs/ft³.The density of the beads will vary with the screen sizing. Oversizedbeads may be ground or shredded to a smaller size and re-screened.

Other sizes of beads may be used, beyond those described above.Different applications typically require different bead sizes. Smallerbeads have more surface area per pound and would tend to be preferredfor lower flow rates of potable and waste water and for lowerconcentrations of contaminants. For higher flow rates it may bepreferable to mix small and large beads together. Larger beads tend toplug or clog less and may be preferred in less accessible locations. Thebeads of the present invention are preferably contained withincontainers such as filter cartridges and other types of POU devices,nylon sacks, porous containers (such as porous plastic or polymercontainers (the plastic or polymer itself being porous) made by orthrough Porex Technolosies of Fairburn, Ga.) and containers with filterpaper or filter material at the inlet and outlet to retain the beads.Such containers, canisters, or columns are known in the art. Potable orwaste water can be flowed over and/or through the beads retained withinsuch containers.

Undersized beads or fines, such as those that pass through U.S. StandardSieve Nos. 100 or 200, have high surface area per pound and may be usedin extruded carbon blocks for potable or waste water treatment. They canalso be used in air filters to remove metal contaminants from airstreams, such as removing lead and heavy metals from smelter air. Inthis application as an air filter the fines or small particles arepreferably dried and physically fixed in a matrix or container, invarious forms and shapes as required by the application, and/or areenclosed such as in filter cloth. etc., or otherwise used to make an airfilter the same way activated carbon is used to make an air filter,which is well-known in the art.

Preferably the beads of the present invention are used to sorb metal andmetalloid ion contaminants such as silver, iron, chromium, cobalt,uranium, mercury, nickel, arsenic, aluminum, cadmium, lead, manganese,copper, zinc and others from dilute aqueous solutions (pH preferably 4to 9, more preferably 6.5 to 8.5, temperature preferably 33°-180° F.,more preferably 50°-100° F.) such as in potable water treatment devicesor in waste water like acid mine drainage waters, in particular wherethe dissolved metals, such as heavy metals and transition metals, haveconcentrations less than 10 ppm, more preferably less than 1 ppm (mg/L),more preferably in the concentration range of 100 to 10 ppb. Thesemetals and metalloids are elemental substances or elements. Suchsorption is accomplished by bringing the dilute aqueous solutions intocontact with the beads. The beads of the present invention are effectiveduring relatively short contact times at 70° F. and at othertemperatures, preferably 1 to 12 minutes, more preferably 2 to 6minutes, in a fixed column. The beads of the present invention exhibitselectivity for heavy metal ions over calcium and magnesium (a usefulcharacteristic since calcium and magnesium frequently interfere withefficiency in this art) but are operable in waste streams with highconcentrations of solids or metal ions. The beads work particularly wellwith copper, lead, zinc, cadmium, and mercury.

The invented beads have many advantages. The activatedcarbon/poly(carboxylic acid) beads are physically strong, waterinsoluble, are made with a non-hazardous, simple process, and both theactivated carbon and binder have metal ion uptake capacity. Theactivated carbon/poly(carboxylic acid), activated carbon/polyamine, andactivated carbon/sodium silicate beads are made using non-hazardousmaterials and using a process which is simple, efficient, inexpensive,and which produces spheroidal beads.

It is believed that the present activated carbon/poly(carboxylic acid)beads will generally remove heavy metal ions at least as well as theactivated carbon/sodium silicate beads, although either are effective.The activated carbon/polyamine beads are typically used for the removalof anionic metals complexes. The poly(carboxylic acid) and polyaminebinders are generally more stable physically than the sodium silicateand may work better where the pH is 8 or higher. The poly(carboxylicacid) and polyamine beads are water-insoluble and are more temperatureresistant and can operate at 120°-180° F., as well as at 32°-120° F. Thesodium silicate beads are preferably used at temperatures below 120° F.;the sodium silicate binder may lose its shape and/or partially dissolvein an aqueous solution at or above 120° F.

The beads of the present invention can be effectively regenerated by (a)passing one to three, preferably two, bed volumes of 1 to 3% HCl throughthe bead-filled container at an upflow rate of 6-10 bed volumes per hour(BV/hr); (b) passing one to three bed volume of H₂O (preferablydeionized) through said container at the same rate. By this techniquevaluable metal contaminants can be recovered from the beads in solutionsamenable to further processing, and regenerated beads can be reused. Thevaluable metal contaminants can subsequently be recovered from thesolutions using techniques known in the art. The invented beads can bereused and cycled through the regeneration procedure many times andstill be effective. It is also possible to run the beads through theabove regeneration procedure prior to the time the beads are first used.This is sometimes referred to as pre-conditioning the beads. Generallyit is not economical to pre-condition the beads prior to their firstuse. Unpre-conditioned beads, on first use, are typically about 80 to95% as efficient as pre-conditioned beads on first use. Whenunpre-conditioned beads are regenerated after first use, they get tonear their peak efficiency. The beads of the present invention willgenerally increase slightly in efficiency through the first few (up toabout 7) regeneration cycles.

The following Examples illustrate various aspects of the presentinvention.

EXAMPLE 1

Sorbent beads were made with powdered activated carbon, poly(acrylicacid) (PAC), and glycerol, formed in a pin mixer and baked in aconvection oven. The resulting beads were (by weight) 79% PAC, 19%Poly(acrylic acid), 1 % glycerol, and 1 % moisture. The beads werescreened to collect the fraction in the −20+50 mesh range. These beadshad a density of 22.8 lb/ft3. This size beads underwent a loadingcapacity test.

The loading capacity is tested with a high concentration lead solutionto determine the amount of lead removed on a known amount of sorbentmaterial. One gram of material was placed in a 1 L beaker with 500 ml ofa lead solution containing 485.5 ppm Pb. The beads were mixed in thesolution for 24 hours. At that point, the lead concentration remainingin solution was 309 ppm Pb. Therefore 1 gram of beads removed 176.5 ppmPb from a 500 ml solution, equal to 87.7 mg/g removal, or 2.01 lb/ft3.This test demonstrates the sorbent material has a high loading capacityfor lead.

EXAMPLE 2

Beads made in Example 1 were tested for kinetics with a copper solutionisotherm. One gram of material was placed in a 1 L beaker with 500 mlcopper solution containing 4.92 ppm Cu. The beads were mixed in solutionfor 4 hours. At that point, the copper concentration remaining insolution was 0.24 ppm Cu. Therefore 95.1% of the copper was removed fromsolution in this time period. This test demonstrates the sorbentmaterial has fast removal kinetics for metal removal.

It should be evident that this disclosure is by way of example and thatvarious changes may be made by adding, modifying or eliminating detailsor elements without departing from the fair scope of the teachingcontained in this disclosure. The invention is therefore not limited toparticular details of this disclosure except to the extent that thefollowing claims are necessarily so limited.

What is claimed is:
 1. A bead comprising 65-94 weight percent activatedcarbon and 4-25 weight percent binder, said binder being effectivelycrosslinked and said activated carbon being effectively immobilized insaid bead, said binder being selected from the group consisting ofpoly(carboxylic acids) and polyamines, said bead being capable ofsorbing a metal or metalloid dissolved in a dilute aqueous solution at aconcentration of less than 10 ppm, said metal or metalloid beingselected from the group consisting of lead, silver, copper, iron,chromium, cobalt, uranium, mercury, nickel, arsenic, aluminum, cadmium,manganese, and zinc.
 2. A bead according to claim 1, wherein said binderis poly(carboxylic acid), said poly(carboxylic acid) binder beingeffectively crosslinked with a crosslinking agent, said crosslinkingagent being a polyalcohol or a mixture of polyalcohols.
 3. A beadaccording to claim 1, wherein said poly(carboxylic acid) is selectedfrom the group consisting of poly(acrylic acid), poly(methacrylic acid),and mixtures thereof.
 4. A bead according to claim 1, wherein saidpoly(carboxylic acid) is poly(acrylic acid).
 5. A bead according toclaim 4, wherein said poly(acrylic acid) has a molecular weight between10,000 and 500,000.
 6. A bead according to claim 2, wherein saidcrosslinking agent is selected from the group consisting of glycerol,ethylene glycol, 1,2-propanediol, 1,3-propanediol, and mixtures thereof.7. A bead according to claim 6, wherein said crosslinking agent isglycerol.
 8. A bead according to claim 1, wherein said activated carbonis bituminous coal-based activated carbon.
 9. A bead according to claim1, wherein said activated carbon is powdered carbon with a particle sizesmaller than 100 mesh.
 10. A bead according to claim 1, wherein saidbinder is polyamine, said polyamine binder being effectively crosslinkedwith a crosslinking agent, said crosslinking agent being a dicarboxylicacid.
 11. A method of making a metal-ion-sorbing bead, said bead beingeffective to sorb metal ions from a dilute aqueous solution, said metalbeing selected from the group consisting of silver, iron, chromium,cobalt, uranium, mercury, nickel, aluminum, cadmium, lead, manganese,copper, and zinc, the method comprising the steps of; a) combiningactivated carbon and a binder solution into a mixture, said bindersolution comprising a binder and a crosslinking agent, said binder beingselected from the group consisting of poly(carboxylic acids) andpolyamines; b) forming the mixture into a first bead comprising 65-94weight percent activated carbon and 4-25 weight percent binder; and c)heating said first bead to effectively crosslink said binder with saidcrosslinking agent to form an effectively crosslinked binder.
 12. Amethod according to claim 11, wherein said binder is poly(carboxylicacid) and said crosslinking agent is a polyalcohol or a mixture ofpolyalcohols.
 13. A method according to claim 11, wherein saidpoly(carboxylic acid,) is selected from the group consisting ofpoly(acrylic acid), poly(methacrylic acid), and mixtures thereof, andwherein said crosslinking agent is selected from the group consisting ofglycerol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, andmixtures thereof.
 14. A method according to claim 13, wherein saidpoly(carboxylic acid) is poly(acrylic acid) and said crosslinking agentis glycerol.
 15. A method according to claim 11, wherein said binder ispolyamine and said crosslinking agent is dicarboxylic acid.
 16. A methodaccording to claim 15, wherein said polyamine is polyethyleneimine andsaid crosslinking agent is glutaric acid.
 17. A method according toclaim 11, wherein said heating takes place in a convection oven.
 18. Amethod according to claim 11, wherein said heating is by radio frequencyheating.
 19. A method according to claim 11, wherein said forming ofsaid mixture is by use of a pin mixer.
 20. A bead according to claim 1,said bead having a diameter of 0.3-1 mm.
 21. A method according to claim11, said binder solution comprising 60-98 weight percent water, 2-40weight percent poly(carboxylic acid), and 0.1-15 weight percentcrosslinking agent.
 22. A bead according to claim 10, wherein saidbinder is polyethylenimine and said crosslinking agent is glutaric acid.23. A bead according to claim 22, said polyethyleneimine having amolecular weight of 60,000-100,000.
 24. A bead according to claim 1,wherein said activated carbon is granular carbon with a particle size of40-80 mesh.
 25. A bead according to claim 5, wherein said poly(acrylicacid) has a molecular weight between 200,000 and 300,000.
 26. A beadaccording to claim 9, wherein said powdered carbon has a particle sizesmaller than 325 mesh.